The Second World War, A conflict that involved virtually every part of the world during the years 1939–45 The Empire of Japan aimed to dominate Asia and the Pacific and was already at war with the Republic of China in 1937, By the early part of 1939 the German dictator Adolf Hitler had become determined to invade and occupy Poland, subsequent declarations of war on Germany by France and the United Kingdom with the subsequent declarations of war on Germany by France and the United Kingdom.